Despite health hazard warnings, studies have indicated that the wearing of high-heeled shoes is a widespread behavior pattern among women. Common foot problems such as callus, plantar forefoot pain, and metatarsal stress fracture were often suffered by women who wear high-heeled shoes. Different studies showed that the plantar pressure distributions are greatly influenced by the increase in heel heights. During walking, high-heeled shoes increased ankle plantar flexion angle, changed muscle activity, reduced gait stability, increased forefoot pressure and possibly increased the risk of knee injuries.
Shoe inserts (removable insole) are commonly used for redistributing the plantar pressure so as to enhance the comfort when wearing shoes. The existing high-heeled shoe inserts are usually made of soft material, e.g. DR. SCHOLL'S° DREAMWALK™ gel inserts, FOOT PETALS® high-heeled shoe insole cushions and INSOLIA® high-heeled shoe insert. These inserts are made with fixed properties, e.g. thickness, shape and hardness. These fixed properties are critical factors of the comfort for the wearer. However, the settings of the existing insert design (i.e. shape and hardness) available in the market are fixed and it may not suitable for everyone or suit different purposes. The level of plantar pressure varies depending on wearer's foot measurement, heel heights and walking condition. Due to the limitation of flexibility, wearers could not adjust the property of inserts for their most desirable comfort condition.
There are various studies on the development of smart insole for footwear, but only few of them were focusing on the insole design for ladies' high-heeled shoes. In the present researches about smart insole for footwear, sensors, which integrated with circuit and electrical power supply, are included to achieve the smart functions. In these designs, sensors are used to determine the plantar pressure distribution and comfort level of the users. Based on the condition, the integrated circuit including sensors changes the property (i.e. shape and hardness) of the smart insole.